Background: Saudi Arabia used to be hyperendemic for HBV infection. Most of infection occurs in early life. HBV vaccine was, therefore, introduced in 1989 as the seventh primary immunogen of the EPI Program. This study is conducted to evaluate the efficacy of this program in Riyadh and Hail Regions. Method and Patients: A cohort follow-up study of children from Riyadh and Hail, who had been vaccinated in 1989, evaluated in 1991 and tested for HBV markers six years later. Results: The files of 303 children from Riyadh and Hail, who were investigated in 1991 retrieved and only 119, were available for testing. Fifty percent of the children have still a protective anti-HBs tittre. One vaccinated child was found to be positive for HBsAg. According to this study, the efficacy rate against HBsAg carriage is 88%. Conclusion: This study demonstrates the tremendous effect of HB vaccine on the HBV infection of Saudi children in these two regions

The endemicity of hepatitis B virus (HBV) in Saudi Arabia is well established[1],[2] . Acquisition of HBV infection occurs mainly by the horizontal route in early life and by the age of ten years, about 7% are HBsAg carriers and about 20% are positive for at least one HBV marker[3],[4] infection contributes significantly to HBV-related morbidity and mortality among Saudi patients[5],[6],[7]

The availability of safe and efficacious HBV vaccine has lead to the feasibility of an effective control of HBV infection especially in HBV endemic countries[8] tegration of HBV vaccine into the expanded program of immunization (EPI) has proved to be a successful strategy[9],[10],[11] . On l st October 1989, a program by which the HBV vaccine was added as the `seventh' primary immunogen of the EPI, was commended in Saudi Arabia)[12] . Included in the program was the creation of a scientific committee to design the implementation strategy, provide technical advice, monitor and evaluate the progress and success of the program. In 1990, another program was also launched by the Ministry of Health to vaccinate all school children. It is anticipated that by 1996, all Saudi children 1-12 years of age will be vaccinated against HBV.

In 1991, an evaluation study of HBV vaccine was undertaken. 637 children from five regions of Saudi Arabia, were investigated. All of them had completed three doses of HB vaccine. 95% of the children were found to have protective anti-HBs without concomitant HBsAg or anti-HBc[12] . In 1997, we performed a second but more detailed randomized community evaluation study. All of the 14 regions of Saudi Arabia were involved. The result of that study has been reported[13] . We used this occasion to conduct a small study following-up children from Riyadh and Hail regions, who were investigated in 1991. The aim of this cohort study is to assess the efficacy of HB vaccine in this population.

Methods and Samples

The files of the 303 children from Riyadh and Hail, who were investigated in 1991, were retrieved. Only 119 out of them were traced (39%). The rest have moved from the region or their old address could not be identified. All specimens were tested for HBsAg, anti-HBc and anti-HBs using the commercially available EIA kits from Abbott laboratories, North Chicago III. The level of anti­HBs expressed in milli international unit per milliliter (ml/mL) were measured by EIA using ANSAB quantitative panel from Abbott laboratories. We used Z-test to compare percentages drawing from different years. A P value <0.05 was judged to reflect a significant difference. P value between 0.05 and 0.1 was judged to reflect a trend.

Results

A total of 119 children (36 from Riyadh and 83 from Hail region) were investigated. According to their record from 1991 study, all of them had seroconverted to anti-HBs with a titre of more than 10 IU/L. Their result now indicates the following:

Only one patient has developed HBsAg infection 59 children lost their anti-HBs status. All the other 60 children still show an anti-HBs with a titre of more than 10 IU/L [Table - 1]. [Figure - 1] shows the comparison of the anti-HBs titre in both studies of 1991 and 1997.

Discussion

This cohort study demonstrates that six years post-vaccination, still 50% of the children in this study have a protective anti-HBs titre (>10 IU.L). This result differs markedly from our major national community study, where the seroconversion rate eight-year after mass vaccination was found to be 70%[13] However, the difference most likely is due to the small sample size of this study and the difference in study design. Only one child has acquired HBsAg infection. According to this result, the efficacy rate against HBsAg carriage is calculated to be 88%.

However, it will be very difficult to draw any important conclusion out of only one case of break through infection. On the other hand, this result go along with similar international study like the Gambian study, where the efficacy rate was found to range between 86% to 98% with an average of 95%[14],[15],[16] . The efficacy rate in our national community based study was calculated to range between 95% to 99%. The reason for this single break through infection is due to the expected rapid decline in the anti-HBs titre[16] . The anti-HBs titre of this infected child in 1991 was 82 IU/L. Comparing the anti-HBs titre value in both studies does not show any correlation between the amount of anti­HBs post-vaccination and lost or decline of that titre.

Conclusion

This study demonstrates again the tremendous effect of HB vaccine on the HBV infection of Saudi children in these two regions. It is expected that the sequel of HBV infection including chronic liver disease and hepatocellular carcinoma will be markedly reduced in the next generation. It shows also that the adopted strategy in Saudi Arabia to include the HB vaccine in EPI programs is very successful.

Acknowledgement

This project was partly supported by Smith-kline Beecham Pharmaceuticals, SB House, Great West Road, and Brentford, England. The authors would like to acknowledge the support of His Excellency, the Minister of Health, Professor Ossama Shobokshi, and all Directors-Generals of Health Regions and Regional Coordinators.